Fri, 12 Aug 2005

Writing the summary of Chapter 2 seemed to work as a warmup for me the other day, so I thought I would write about Chapter 3 as a warm up for working some more on Chapter 7. I also need to look at reviewer comments for Chapters 2, 3, and 4 sometime today, so it seems like a good idea as well because it will help me remember what I am trying to cover in the chapter.

Chapter 3 is all about the different things you can do with compression with ImageMagick, as well as other forms of image metadata. So, I start out by talking about lossy versus lossless compression (there's an interesting tangent to this discussion which I need to add as a sidebar to the chapter during this editing process, but I'll leave that to another post here), I give some examples of the accumulative nature of the loss from lossy compressions. We then move on to compare the size of a bunch of images using different compression algorithms, which gives a good introduction to discussing which image format is the right choice for given scenarios.

(As an aside that I will follow here, that was probably the most recurrent battle I used to fight as an imaging specialist at IPAustralia, what format to use when. The number of times I've had to explain why JPEG is a poor choice for text is amazing to me.)

I also talk about other compression aspects, such as quality levels and interlacing.

Then we talk about image metadata, which includes random stuff like image width and height, as well as more complicated stuff like JPEG's EXIF tags. It also includes changing what imaging nerds would call the photometric interpretation -- the way that the pixels are interpreted in the image. For example with a black and white image, is 0 black, or white? I finish up by briefing covering gamma correction, color intent and profiles, and so forth.

Finally, I introduce multiple image formats, such as TIFF, and PDF, which can have more than one image per file. Animations are of course multiple image formats as well.